[NFC] Use llvm::TrailingObjects to represent variable list of lifetime sources

Author: meg-gupta

include/swift/AST/LifetimeDependence.h

@@ -26,6 +26,7 @@
 #include "swift/Basic/SourceLoc.h"
 
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/Support/TrailingObjects.h"
 
 namespace swift {
 
@@ -137,22 +138,30 @@ struct LifetimeDescriptor {
   }
 };
 
-// TODO: Use TrailingObjects to tail allocate sources
-class LifetimeEntry {
+class LifetimeEntry final
+    : private llvm::TrailingObjects<LifetimeEntry, LifetimeDescriptor> {
+  friend TrailingObjects;
+
 private:
   SourceLoc startLoc, endLoc;
-  ArrayRef<LifetimeDescriptor> sources;
+  unsigned numSources;
   std::optional<LifetimeDescriptor> targetDescriptor;
 
   LifetimeEntry(
       SourceLoc startLoc, SourceLoc endLoc,
       ArrayRef<LifetimeDescriptor> sources,
       std::optional<LifetimeDescriptor> targetDescriptor = std::nullopt)
-      : startLoc(startLoc), endLoc(endLoc), sources(sources),
-        targetDescriptor(targetDescriptor) {}
+      : startLoc(startLoc), endLoc(endLoc), numSources(sources.size()),
+        targetDescriptor(targetDescriptor) {
+    std::uninitialized_copy(sources.begin(), sources.end(),
+                            getTrailingObjects<LifetimeDescriptor>());
+  }
+
+  size_t numTrailingObjects(OverloadToken<LifetimeDescriptor>) const {
+    return numSources;
+  }
 
 public:
-  /// \p sources should be allocated on the ASTContext
   static LifetimeEntry *
   create(const ASTContext &ctx, SourceLoc startLoc, SourceLoc endLoc,
          ArrayRef<LifetimeDescriptor> sources,
@@ -162,14 +171,14 @@ class LifetimeEntry {
   SourceLoc getStartLoc() const { return startLoc; }
   SourceLoc getEndLoc() const { return endLoc; }
 
-  ArrayRef<LifetimeDescriptor> getSources() const { return sources; }
+  ArrayRef<LifetimeDescriptor> getSources() const {
+    return {getTrailingObjects<LifetimeDescriptor>(), numSources};
+  }
 
   std::optional<LifetimeDescriptor> getTargetDescriptor() const {
     return targetDescriptor;
   }
 
-  bool empty() const { return !sources.empty(); }
-
   std::string getString() const {
     std::string result = "@lifetime(";
     if (targetDescriptor.has_value()) {
@@ -178,7 +187,7 @@ class LifetimeEntry {
     }
 
     bool firstElem = true;
-    for (auto source : sources) {
+    for (auto source : getSources()) {
       if (!firstElem) {
         result += ", ";
       }

lib/AST/LifetimeDependence.cpp

@@ -29,7 +29,8 @@ LifetimeEntry *
 LifetimeEntry::create(const ASTContext &ctx, SourceLoc startLoc,
                       SourceLoc endLoc, ArrayRef<LifetimeDescriptor> sources,
                       std::optional<LifetimeDescriptor> targetDescriptor) {
-  void *mem = ctx.Allocate(sizeof(LifetimeEntry), alignof(LifetimeEntry));
+  unsigned size = totalSizeToAlloc<LifetimeDescriptor>(sources.size());
+  void *mem = ctx.Allocate(size, alignof(LifetimeEntry));
   return new (mem) LifetimeEntry(startLoc, endLoc, sources, targetDescriptor);
 }
 

lib/Parse/ParseDecl.cpp

@@ -5210,7 +5210,7 @@ ParserResult<LifetimeEntry> Parser::parseLifetimeEntry(SourceLoc loc) {
   }
 
   auto *lifetimeEntry = LifetimeEntry::create(
-      Context, loc, rParenLoc, Context.AllocateCopy(sources), targetDescriptor);
+      Context, loc, rParenLoc, sources, targetDescriptor);
   return ParserResult<LifetimeEntry>(lifetimeEntry);
 }